1. Field of the Invention
The present invention relates generally to rotary valves and, more particularly, to apparatus and methods especially suitable for a plug valve with a telescoping seat assembly.
2. Description of the Background
Telescoping seat assemblies have been known for use in gate valves for some time. One advantage of this type of seat assembly, as used in gate valves, is the ability to provide a force on the seats and valve body that varies due to pressures encountered. In this way, one is assured of a good seal with a wide range of pressures without excessive friction. Another highly desirable advantage is the possibility of upstream and downstream seals to increase valve reliability.
However, products for rotary valves such as plug valves, have not yet been able to take advantage of the benefits of telescoping seat assemblies. Techniques and construction have not been developed and the reasons for failures when attempts to use these types of seating assemblies have not been understood well enough to allow transfer of this technology from gate valves to rotary valves such as plug valves. The possibility of having the advantages of reliable upstream and downstream sealing would be especially useful if it were possible to use telescoping seating assemblies with rotary valves.
Instead, other constructions have been used to produce plug valves. These valves do not have the advantage of upstream and downstream sealing that increases the reliability of operation. One type of plug valve uses a wedge type of sealing force along with significant lubrication to maintain a primary seal whereby the plug has a taper and a nut is used to wedge the seals into the valve body adjacent the plug. However, after opening and closing several times sometimes the sealing may be less reliable. Another type of plug valve uses a floating plug that produces a downstream seal. If that seal should be lost, then there is no secondary seal to prevent leakage.
Telescoping seat assemblies in the past have relied on O-ring seals which use elastomeric material. Such O-ring seals have the advantage of being easy to effect good sealing with loose tolerances. However, when a device may be used in a wide range of temperatures, fluids, and pressures, it becomes highly difficult to ascertain that the proper O-ring will be used. Numerous types of O-rings exist with each type being suitable for different ranges of tolerances, pressures, and temperatures. The charts which have all these effects are quite complex and one must know beforehand the specific fluids, pressures, and temperatures for the application to select the correct O-ring. O-rings are also subject to the phenomena of explosive decompression when high pressures are suddenly reduced due to expansion of gas that has permeated into the O-ring. Because valves are used for a wide variety of purposes, it becomes highly probable that in some cases depending on the fluid, pressure, and temperature the wrong O-rings will be used for a particular application and the valve will leak.
Unidirectional seals made of non-elastomeric and non-permeable materials have been known that will operate under much wider ranges of temperatures, fluids, and pressures than O-rings. However, such seals do not easily effect a seal as do O-rings. The tolerances must be much tighter and the surfaces cannot tolerate imperfections. For this and related reasons, the use of non-elastomeric materials has been greatly limited. For the same reason, TEFLON based seals are not widely used even though they are inert to virtually any fluid. Such seals do not simply replace an O-ring. In fact, it is believed that these seals create additional difficulties and so have never been operational in a telescoping seat assembly prior to the invention of the parent to this application. Prior to the present invention, such seals are not known to have been used in rotary valves.
An exemplary type of telescoping valve seat assembly gate valve is shown in U.S. Pat. No. 4,878,651, issued Nov. 7, 1989, to F. W. Meyer, Jr., which is incorporated herein by reference, as a through conduit gate valve apparatus with a valve seat assembly that is field maintainable and which prevents the occurrence of pressure lock. Each valve seat assembly includes a retainer ring fixed in the valve body and a pressure responsive seat ring that seals with the gate member. The seat ring is responsive to fluid pressure in the valve flow passageways for maintaining and enhancing the face seal with the gate and simultaneously to fluid pressure in the valve chamber for automatically venting the valve chamber to present occurrence of a pressure lock condition.
Another telescoping valve seat assembly gate valve is shown in U.S. Pat. No. 5,201,872, issued Apr. 13, 1993, to M. L. Dyer, which is also incorporated herein by reference, that discloses a gate valve wherein bore pressure in the body cavity of the valve is isolated in the open and closed position. In the closed position, a double metal sealing barrier is provided across the gate. In the open position, the pressure is isolated from the stem packing and bonnet gasket by the seats on either side of the gate. Formation of hydrates in the body cavity is eliminated, and better retention of body grease is achieved during flow through the valves. Metal-to-metal seal surfaces are developed, thereby eliminating wear on the nonmetal components and reducing torque requirements.
Thus, it would be desirable to provide for the advantages of telescoping seating assemblies in a rotary valve such as a plug valve. Those skilled in the art have long sought and will appreciate the present invention which addresses these and other problems.
A rotary plug valve for controlling a line pressure is disclosed herein that comprises a valve body having a valve chamber therein. First and second passages, such as inlets and outlets, extend through the valve body and are in communication with the valve chamber to define a flow passage through the valve body. The valve is preferably bidirectional so that either end of the valve may be the upstream or downstream end. The valve body has recesses that surround the flow passages adjacent to the valve chamber. In a preferred embodiment, a cylindrical plug is mounted in the valve chamber for controlling flow through the valve body. The cylindrical plug has a first curved seal surface. A telescoping seat assembly is preferably provided in each of the recesses. Each telescoping seat assembly may include a first seat element that defines a second curved seal surface for engaging the first curved seal surface and a second seat element for engaging and sealing with the recess. The first seat element and the second seat element may be relatively moveable with respect to each other. A valve stem is provided for rotating the cylindrical plug. The cylindrical plug may be connected with the valve stem and may be secured within the valve chamber of the valve body so as to be laterally moveable in the direction the telescoping seat assemblies.
A connection between the valve stem and the cylindrical plug preferably permits the cylindrical plug to be moveable laterally toward first and the second passages. The connection may comprise a pin and socket connection wherein the pin is moveable in a least one lateral direction within the socket. In a preferred embodiment, the cylindrical plug may be secured within the valve chamber of the valve body so as to be moveable with respect to the telescoping seat assemblies when the valve is in the closed position. Thus, movement of the cylindrical plug is more restricted when the cylindrical plug is in the open position.
A line pressure area is preferably provided on the first seat element for receiving line pressure to produce a contact stress between the first curved seal surface of the cylindrical plug and the second curved seal surface of the first seat element. The contact stress varies due to location along the first and second curved sealing surfaces because of a curvature thereof. The line pressure area on the first seat element may be large enough such that the contact stress is greater than the line pressure over a sufficient portion of the first and second curved seal surfaces to produce a gas tight seal. In one embodiment, the line pressure area on the first seat element may be large enough such that an average contact stress along the first and second curved seal surfaces is greater than the line pressure.
The present invention comprises a method of making/assembling a rotary valve for controlling a line pressure that comprises providing a valve body with a valve chamber therein and providing first and second passages that extend through the plug valve body and which are in communication with the valve chamber to define a flow path through the valve body. A first recess is provided surrounding the first passage adjacent to the gate chamber and a second recess surrounding the second passage adjacent to the gate chamber. A rotary valve element is provided for the valve chamber that is rotatably moveable between an open position and a closed position.
A valve stem is provided for rotating the rotary valve closure element. A first telescoping seat assembly with first and second seat elements is provided for the first recess and a second telescoping assembly with first and second seat elements for the second recess. A line pressure surface is provided in the first telescoping seat assembly to thereby expand the first and second seat elements of the first telescoping seat assembly outwardly with respect to each other to form a seal with the rotary valve element and with the first pocket. A connection between the valve stem and the rotary valve element is provided that permits lateral movement of the rotary valve element with respect to the valve stem to thereby permit the rotary valve element to compress the first and second seat elements of the second telescoping seat assembly due to pressure on the rotary valve element when the rotary valve element is in the closed position to thereby seal with the rotary valve element and the second pocket.
A first curved seal surface is provided for the cylindrical plug and a second curved seal surface is provided on the first seat element such that a contact stress arises between the first curved seal surface and the second curved seal surface due to the line pressure acting on the line pressure surface. The contract stress varies depending on location along the first and second curved seal surfaces because of a curvature thereof. The line pressure surface on the first seat element may be large enough such that the contact stress is greater than the line pressure over a sufficient portion of the first and second curved seal surfaces to produce a fluid tight seal.
The connection between the valve stem and rotary valve element may preferably allow extended lateral movement when the rotary valve is in the closed position as compared with the open position.
A bonnet may be secured within the valve body and may be removable through a service opening in the valve body. A cylindrical plug is mounted in the valve chamber and rotatable between and open and closed position. The valve stem seal and valve stem bearing surrounding the valve stem may preferably be mounted within the bonnet. The valve stem seal and the valve stem bearing and the valve stem and the bonnet may preferably be removable as a unit through the service opening in the valve body.
It is an object of the present invention to provide an improved seat assembly for a rotary valve and especially a rotary plug valve.
Yet another object of the present invention is to provide an embodiment of the invention that may be used over wider ranges of temperature, pressure, and fluid types.
An advantage of the present invention, in a preferred embodiment, is increased reliability due to the valve preferably having both an upstream seal and a downstream seal.
These and other objects, features, and advantages of the present invention will become apparent from the drawings, the descriptions given herein, and the appended claims. The above summary and any listed objects are provided only to list information about the invention in a quickly reviewable form and are therefore not intended to limit the invention in any way not shown by the appended claims of the invention that lists features thereof and any equivalents thereof.